.\" $OpenBSD: ECDSA_SIG_new.3,v 1.15 2019/08/25 14:11:41 schwarze Exp $
.\" full merge up to: OpenSSL e9b77246 Jan 20 19:58:49 2017 +0100
.\" selective merge up to: OpenSSL da4ea0cf Aug 5 16:13:24 2019 +0100
.\"
.\" This file was written by Nils Larsch <nils@openssl.org>.
.\" Copyright (c) 2004, 2005, 2013, 2016 The OpenSSL Project.
.\" All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\"
.\" 1. Redistributions of source code must retain the above copyright
.\"    notice, this list of conditions and the following disclaimer.
.\"
.\" 2. Redistributions in binary form must reproduce the above copyright
.\"    notice, this list of conditions and the following disclaimer in
.\"    the documentation and/or other materials provided with the
.\"    distribution.
.\"
.\" 3. All advertising materials mentioning features or use of this
.\"    software must display the following acknowledgment:
.\"    "This product includes software developed by the OpenSSL Project
.\"    for use in the OpenSSL Toolkit. (http://www.openssl.org/)"
.\"
.\" 4. The names "OpenSSL Toolkit" and "OpenSSL Project" must not be used to
.\"    endorse or promote products derived from this software without
.\"    prior written permission. For written permission, please contact
.\"    openssl-core@openssl.org.
.\"
.\" 5. Products derived from this software may not be called "OpenSSL"
.\"    nor may "OpenSSL" appear in their names without prior written
.\"    permission of the OpenSSL Project.
.\"
.\" 6. Redistributions of any form whatsoever must retain the following
.\"    acknowledgment:
.\"    "This product includes software developed by the OpenSSL Project
.\"    for use in the OpenSSL Toolkit (http://www.openssl.org/)"
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE OpenSSL PROJECT ``AS IS'' AND ANY
.\" EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
.\" PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE OpenSSL PROJECT OR
.\" ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
.\" SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
.\" LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
.\" STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
.\" OF THE POSSIBILITY OF SUCH DAMAGE.
.\"
.Dd $Mdocdate: August 25 2019 $
.Dt ECDSA_SIG_NEW 3
.Os
.Sh NAME
.Nm ECDSA_SIG_new ,
.Nm ECDSA_SIG_free ,
.Nm ECDSA_SIG_get0 ,
.Nm ECDSA_SIG_set0 ,
.Nm i2d_ECDSA_SIG ,
.Nm d2i_ECDSA_SIG ,
.Nm ECDSA_size ,
.Nm ECDSA_sign_setup ,
.Nm ECDSA_sign ,
.Nm ECDSA_sign_ex ,
.Nm ECDSA_verify ,
.Nm ECDSA_do_sign ,
.Nm ECDSA_do_sign_ex ,
.Nm ECDSA_do_verify ,
.Nm ECDSA_OpenSSL ,
.Nm ECDSA_get_default_method ,
.Nm ECDSA_set_default_method ,
.Nm ECDSA_set_method
.Nd Elliptic Curve Digital Signature Algorithm
.Sh SYNOPSIS
.In openssl/ecdsa.h
.Ft ECDSA_SIG*
.Fo ECDSA_SIG_new
.Fa void
.Fc
.Ft void
.Fo ECDSA_SIG_free
.Fa "ECDSA_SIG *sig"
.Fc
.Ft void
.Fo ECDSA_SIG_get0
.Fa "const ECDSA_SIG *sig"
.Fa "const BIGNUM **r"
.Fa "const BIGNUM **s"
.Fc
.Ft int
.Fo ECDSA_SIG_set0
.Fa "ECDSA_SIG *sig"
.Fa "BIGNUM *r"
.Fa "BIGNUM *s"
.Fc
.Ft int
.Fo i2d_ECDSA_SIG
.Fa "const ECDSA_SIG *sig_in"
.Fa "unsigned char **der_out"
.Fc
.Ft ECDSA_SIG*
.Fo d2i_ECDSA_SIG
.Fa "ECDSA_SIG **sig_out"
.Fa "const unsigned char **der_in"
.Fa "long len"
.Fc
.Ft int
.Fo ECDSA_size
.Fa "const EC_KEY *eckey"
.Fc
.Ft int
.Fo ECDSA_sign_setup
.Fa "EC_KEY *eckey"
.Fa "BN_CTX *ctx"
.Fa "BIGNUM **kinv"
.Fa "BIGNUM **rp"
.Fc
.Ft int
.Fo ECDSA_sign
.Fa "int type"
.Fa "const unsigned char *dgst"
.Fa "int dgstlen"
.Fa "unsigned char *sig"
.Fa "unsigned int *siglen"
.Fa "EC_KEY *eckey"
.Fc
.Ft int
.Fo ECDSA_sign_ex
.Fa "int type"
.Fa "const unsigned char *dgst"
.Fa "int dgstlen"
.Fa "unsigned char *sig"
.Fa "unsigned int *siglen"
.Fa "const BIGNUM *kinv"
.Fa "const BIGNUM *rp"
.Fa "EC_KEY *eckey"
.Fc
.Ft int
.Fo ECDSA_verify
.Fa "int type"
.Fa "const unsigned char *dgst"
.Fa "int dgstlen"
.Fa "const unsigned char *sig"
.Fa "int siglen"
.Fa "EC_KEY *eckey"
.Fc
.Ft ECDSA_SIG*
.Fo ECDSA_do_sign
.Fa "const unsigned char *dgst"
.Fa "int dgst_len"
.Fa "EC_KEY *eckey"
.Fc
.Ft ECDSA_SIG*
.Fo ECDSA_do_sign_ex
.Fa "const unsigned char *dgst"
.Fa "int dgstlen"
.Fa "const BIGNUM *kinv"
.Fa "const BIGNUM *rp"
.Fa "EC_KEY *eckey"
.Fc
.Ft int
.Fo ECDSA_do_verify
.Fa "const unsigned char *dgst"
.Fa "int dgst_len"
.Fa "const ECDSA_SIG *sig"
.Fa "EC_KEY* eckey"
.Fc
.Ft const ECDSA_METHOD*
.Fo ECDSA_OpenSSL
.Fa void
.Fc
.Ft const ECDSA_METHOD*
.Fo ECDSA_get_default_method
.Fa void
.Fc
.Ft void
.Fo ECDSA_set_default_method
.Fa "const ECDSA_METHOD *meth"
.Fc
.Ft int
.Fo ECDSA_set_method
.Fa "EC_KEY *eckey"
.Fa "const ECDSA_METHOD *meth"
.Fc
.Sh DESCRIPTION
These functions provide a low level interface to ECDSA.
Most applications should use the higher level EVP interface such as
.Xr EVP_DigestSignInit 3
or
.Xr EVP_DigestVerifyInit 3
instead.
Creation of the required
.Vt EC_KEY
objects is described in
.Xr EC_KEY_new 3 .
.Pp
The
.Vt ECDSA_SIG
structure consists of two
.Vt BIGNUM Ns s
for the
.Fa r
and
.Fa s
value of an ECDSA signature (see X9.62 or FIPS 186-2).
.Bd -literal -offset indent
struct {
	BIGNUM *r;
	BIGNUM *s;
} ECDSA_SIG;
.Ed
.Pp
.Fn ECDSA_SIG_new
allocates a new
.Vt ECDSA_SIG
structure (note: this function also allocates the
.Vt BIGNUM Ns s )
and initializes it.
.Pp
.Fn ECDSA_SIG_free
frees the
.Vt ECDSA_SIG
structure
.Fa sig .
.Pp
.Fn ECDSA_SIG_get0
retrieves internal pointers the
.Fa r
and
.Fa s
values contained in
.Fa sig .
.Pp
.Fn ECDSA_SIG_set0
sets the
.Fa r
and
.Fa s
values in
.Fa sig .
Calling this function transfers the memory management of the values to
.Fa sig .
Therefore, the values that have been passed in
should not be freed by the caller.
.Pp
.Fn i2d_ECDSA_SIG
creates the DER encoding of the ECDSA signature
.Fa sig_in
and writes the encoded signature to
.Pf * Fa der_out .
.Fn d2i_ECDSA_SIG
decodes the DER-encoded signature stored in the buffer
.Pf * Fa der_in
which is
.Fa len
bytes long into
.Pf * Fa sig_out .
For details about the semantics, examples, caveats, and bugs, see
.Xr ASN1_item_d2i 3 .
.Pp
.Fn ECDSA_size
returns the maximum length of a DER-encoded ECDSA signature created with
the private EC key
.Fa eckey .
.Pp
.Fn ECDSA_sign_setup
may be used to precompute parts of the signing operation.
.Fa eckey
is the private EC key and
.Fa ctx
is a pointer to a
.Vt BN_CTX
structure (or
.Dv NULL ) .
The precomputed values are returned in
.Fa kinv
and
.Fa rp
and can be used in a later call to
.Fa ECDSA_sign_ex
or
.Fa ECDSA_do_sign_ex .
.Pp
.Fn ECDSA_sign
is a wrapper function for
.Fa ECDSA_sign_ex
with
.Fa kinv
and
.Fa rp
set to
.Dv NULL .
.Pp
.Fn ECDSA_sign_ex
computes a digital signature of the
.Fa dgstlen
bytes hash value
.Fa dgst
using the private EC key
.Fa eckey
and the optional pre-computed values
.Fa kinv
and
.Fa rp .
The DER-encoded signature is stored in
.Fa sig
and its length is returned in
.Fa siglen .
Note:
.Fa sig
must point to
.Fn ECDSA_size
bytes of memory.
The parameter
.Fa type
is ignored.
.Pp
.Fn ECDSA_verify
verifies that the signature in
.Fa sig
of size
.Fa siglen
is a valid ECDSA signature of the hash value
.Fa dgst
of size
.Fa dgstlen
using the public key
.Fa eckey .
The parameter
.Fa type
is ignored.
.Pp
.Fn ECDSA_do_sign
is a wrapper function for
.Fn ECDSA_do_sign_ex
with
.Fa kinv
and
.Fa rp
set to
.Dv NULL .
.Pp
.Fn ECDSA_do_sign_ex
computes a digital signature of the
.Fa dgst_len
bytes hash value
.Fa dgst
using the private key
.Fa eckey
and the optional pre-computed values
.Fa kinv
and
.Fa rp .
The signature is returned in a newly allocated
.Vt ECDSA_SIG
structure (or
.Dv NULL
on error).
.Pp
.Fn ECDSA_do_verify
verifies that the signature
.Fa sig
is a valid ECDSA signature of the hash value
.Fa dgst
of size
.Fa dgst_len
using the public key
.Fa eckey .
.Sh RETURN VALUES
.Fn ECDSA_SIG_new
returns the new
.Vt ECDSA_SIG
object or
.Dv NULL
if an error occurs.
.Pp
.Fn i2d_ECDSA_SIG
returns the number of bytes successfully encoded
or a negative value if an error occurs.
.Pp
.Fn d2i_ECDSA_SIG
returns a pointer to the decoded
.Vt ECDSA_SIG
structure or
.Dv NULL
if an error occurs.
.Pp
.Fn ECDSA_size
returns the maximum length signature or 0 on error.
.Pp
.Fn ECDSA_SIG_set0 ,
.Fn ECDSA_sign ,
.Fn ECDSA_sign_ex ,
and
.Fn ECDSA_sign_setup
return 1 if successful or 0 on error.
.Pp
.Fn ECDSA_do_sign
and
.Fn ECDSA_do_sign_ex
return a pointer to an allocated
.Vt ECDSA_SIG
structure or
.Dv NULL
on error.
.Pp
.Fn ECDSA_verify
and
.Fn ECDSA_do_verify
return 1 for a valid signature, 0 for an invalid signature and -1 on
error.
The error codes can be obtained by
.Xr ERR_get_error 3 .
.Sh EXAMPLES
Creating an ECDSA signature of given SHA-1 hash value using the named
curve secp192k1.
.Pp
First step: create an
.Vt EC_KEY
object.
This part is
.Em not
ECDSA specific.
.Bd -literal -offset indent
int ret;
ECDSA_SIG *sig;
EC_KEY *eckey;

eckey = EC_KEY_new_by_curve_name(NID_secp192k1);
if (eckey == NULL) {
	/* error */
}
if (!EC_KEY_generate_key(eckey)) {
	/* error */
}
.Ed
.Pp
Second step: compute the ECDSA signature of a SHA-1 hash value using
.Fn ECDSA_do_sign
.Bd -literal -offset indent
sig = ECDSA_do_sign(digest, 20, eckey);
if (sig == NULL) {
	/* error */
}
.Ed
.Pp
or using
.Fn ECDSA_sign
.Bd -literal -offset indent
unsigned char *buffer, *pp;
int buf_len;

buf_len = ECDSA_size(eckey);
buffer  = malloc(buf_len);
pp = buffer;
if (!ECDSA_sign(0, dgst, dgstlen, pp, &buf_len, eckey) {
	/* error */
}
.Ed
.Pp
Third step: verify the created ECDSA signature using
.Fn ECDSA_do_verify
.Pp
.Dl ret = ECDSA_do_verify(digest, 20, sig, eckey);
.Pp
or using
.Fn ECDSA_verify
.Pp
.Dl ret = ECDSA_verify(0, digest, 20, buffer, buf_len, eckey);
.Pp
and finally evaluate the return value:
.Bd -literal -offset indent
if (ret == -1) {
	/* error */
} else if (ret == 0) {
	/* incorrect signature */
} else {
	/* ret == 1 */
	/* signature ok */
}
.Ed
.Sh SEE ALSO
.Xr crypto 3 ,
.Xr d2i_ECPKParameters 3 ,
.Xr DSA_new 3 ,
.Xr EC_GROUP_new 3 ,
.Xr EC_KEY_METHOD_new 3 ,
.Xr EC_KEY_new 3 ,
.Xr ECDSA_set_ex_data 3 ,
.Xr EVP_DigestSignInit 3 ,
.Xr EVP_DigestVerifyInit 3 ,
.Xr RSA_new 3
.Sh STANDARDS
ANSI X9.62, US Federal Information Processing Standard FIPS 186-2
(Digital Signature Standard, DSS)
.Sh HISTORY
.Fn ECDSA_SIG_new ,
.Fn ECDSA_SIG_free ,
.Fn i2d_ECDSA_SIG ,
.Fn d2i_ECDSA_SIG ,
.Fn ECDSA_size ,
.Fn ECDSA_sign_setup ,
.Fn ECDSA_sign ,
.Fn ECDSA_sign_ex ,
.Fn ECDSA_verify ,
.Fn ECDSA_do_sign ,
.Fn ECDSA_do_sign_ex ,
.Fn ECDSA_do_verify ,
.Fn ECDSA_OpenSSL ,
.Fn ECDSA_get_default_method ,
.Fn ECDSA_set_default_method ,
and
.Fn ECDSA_set_method
first appeared in OpenSSL 0.9.8 and have been available since
.Ox 4.5 .
.Pp
.Fn ECDSA_SIG_get0
and
.Fn ECDSA_SIG_set0
first appeared in OpenSSL 1.1.0 and have been available since
.Ox 6.3 .
.Sh AUTHORS
.An Nils Larsch
for the OpenSSL project.
